This invention relates in general to a mounting arrangement which dampens acoustical noise and vibration resulting from the operation of a hydraulic control unit for a vehicular braking system.
Anti-lock braking systems are used in vehicles to maintain control and prevent wheel lock-up under adverse conditions such as rain, snow or ice. The speed of the vehicle's wheels is monitored and application of hydraulic pressure to the brakes is controlled. Anti-lock brake systems typically include a hydraulic control unit which cyclically relieves and reapplies pressure to the brakes through a plurality of solenoid actuated valves housed in the unit. The hydraulic control unit may also house a motor driven reciprocating pump which supplies pressurized brake fluid for operation of the system. The operation of the solenoid valves and reciprocating pump generates vibrations which can be objectionable to vehicle occupants. In particular, the vibrations are caused by the opening and closing of the solenoid valves and the reactionary forces caused by the motor's rotation. These vibrations generate an acoustical noise which consists of sound energy transmitted through the air and vehicle body members to the passenger compartment.
A mounting bracket having several mounting arms is typically used to fasten the hydraulic control unit to the vehicle body. A grommet is placed on each mounting arm between the hydraulic control unit and the surface of the mounting arm. Each grommet is formed from a resilient elastomeric material, such as rubber, for supporting and isolating the hydraulic control unit from the mounting bracket.
An example of a prior art mounting arrangement for attaching a hydraulic control unit to a vehicle body is shown in FIG. 1. The mounting arrangement includes a mounting bracket support arm 10 having an annular indentation portion 12. The indentation portion 12 has an opening 14 through which a stud 16 extends. The stud 16 includes a hexagonal shaped head 18 having six associated edges 19 and a threaded portion 20. The stud 16 is threadedly fastened to a hydraulic control unit 22. A rubber grommet 24 is located between the indentation portion 12 of the support arm 10 and the stud 16. The grommet 24 has a circular hole 26 having an internal cylindrical wall for receiving the hexagonal bead 18 of the stud 16. The six associated edges 19 of the hexagonal head 18 separately contact the cylindrical wall of the grommet 24. Vibrations generated by the hydraulic control unit 22 are transmitted through the edges and are dampened by the rubber grommet 24.
Another example of a prior art mounting arrangement is shown in FIG. 2 and includes a mounting bracket support arm 30 having a hole 32 and a generally cylindrical rubber grommet 34. The grommet 34 has an outer annular groove 36 which extends circumferentially around the grommet 34. The grommet 34 has a central hole 38 through which a tubular metal retaining sleeve 40 is inserted. The retaining sleeve 40 has a flanged outer end 42 which cooperates with a mounting bolt 44 to fasten the hydraulic control unit 22 relative to the support arm 30. An undesirable effect of tightening the bolt 44 is the compression of the rubber grommet 34 by the flanged end 42 of the retaining sleeve 40. This compression reduces the dampening capabilities by decreasing the flexibility of the rubber grommet 34.